This invention relates generally to a soldering apparatus of a type in which an article to be soldered, traveling along a predetermined path, is brought into contact with a flowing layer of a molten solder and, more specifically, to a soldering apparatus of the above-mentioned type in which the height of the solder layer may be automatically adjusted within a predetermined range.
There is a known apparatus for soldering articles, such as printed circuit boards, traveling along a predetermined path of travel, which includes a vessel for containing a molten solder, a pump, and a solder applicator disposed in the vessel and having an injection nozzle or an overflow opening from which the molten solder in the vessel is ejected, upon driving of the pump, to form a wave or layer of the molten solder with which the article is contacted during its travel over the nozzle. The height of the upper surface of the wave or layer of the molten solder is maintained constant during the operation of the pump at a constant speed. However, the height of the upper surface of the solder layer is occasionally lowered due to, for example, consumption of the molten solder by soldering and oxidation. Therefore, it is necessary to control the operation speed of the pump in order to maintain the upper surface of the solder layer at a constant level.
Thus, one known apparatus uses two electrodes positioned at predetermined upper and lower levels and each adapted for generating a detecting signal when it is brought into contact with the solder layer. On the basis of the detecting signal, the operation speed of a pump is increased or decreased so as to maintain the upper surface of the solder layer between the upper and lower levels. In this case, however, the positions of the tip of the electrodes change when the solder deposits thereon. This adversely affects the precise control of the solder layer. Further, the deposits are oxidized by contact with air to form an electrically insulating film so that the electrodes fail to detect the upper level of the solder layer even if they come into contact with the solder layer. Therefore, in order to precisely control the level of the solder layer, it is necessary to remove the solder deposits from the electrodes as soon as possible. This is, however, troublesome and does not meet with automatic control of the level of the solder layer.